隨著網際網路日益的發達，越來越多的資料都以數位的方式貯存以加速資料的傳輸及交流，而在這公開的網路傳輸過程中，常常會有安全上的顧慮，於是有很多資料隱藏的技術就相繼被提出。有別於一般密碼學的方式，我們不是將欲傳資訊以加密的方式來防範攻擊行為，而是以藏於偽裝媒介的方式來達成傳輸祕密資訊的目的。
本論文提出了三種不同的資料隱藏的技術，分別在空間域及頻率域上將資訊隱藏於偽裝影像之中，在空間域中。我們提出了二種基於LSB資料隱藏方法。這兩種方法可以再進一步地將之分類為固定及非固定的LSB取代法，而其中一個是根據欲藏資料排列關係的方式，來取代LSB並且給予適合的補償以降低失真;另一個則是以Lie及Chang [11]等人所提出的方法作為基礎，並應用了OPAP[3]來將之改良。而在頻率域中，我們提出一個基於JEPG壓縮的資訊隱藏方法，利用DCT量化的特性，我們可以更變中頻為零的係數，並將其置換為欲藏的資訊，並於解出資訊的同時，我們可以再將偽裝影像回復成最初的JPEG檔案，當中我們更應用了NAF[22,24]的特性來讓影像的壓縮率及PSNR提升。我們提出的方法都是不需要參照原圖就能解出隱藏的訊息，在實驗中也證實我們的方法的確可讓偽裝影像在人眼分辨不出有異的情況下，達到高容量資訊隱藏的目的。

With the fast advent of internet, many of data are converted to digital format in order to accelerate communication. However, it leads more consideration on security. Therefore a lot of data hiding techniques are proposed. Unlike cryptography, the secret information is not encrypted to prevent malicious behavior, but it used the cover media to embed the secret information for the sake of the secret communication.
In this thesis, we proposed three different data hiding schemes. The first two are based on the spatial domain, they can be classified fixed and unfixed LSBs substitution methods. The first one utilizes the arrangement of the secret data to compensate distortion. And the second proposed technique uses OPAP [3] to improve Lie and Chang proposed scheme [11]. The last one is based on JPEG compression, it utilizes the characteristic of DCT quantization. Therefore we can hide our secret message by adjusting the zero coefficients corresponding to medium frequencies. Besides, we can obtain original JPEG file after retrieving the secret data. In addition, we can enhance the performance of compression by adopting NAF [22, 24]. Both of these methods are no need of referencing the original image when extracting the hided data form the stego-image. Our experimental results will show the proposed method can reach the high capacity with good image quality.

[1] D. Artz, “Digital Steganography: Hiding data within data,” IEEE Internet Computing , vol.5,pp. 75-80, May-June 2001.
[2] W. Bender, D. Gruhl, N. Morimoto and A. Lu, “Techniques for data hiding ,” IBM system Journal, Vol. 35, No. 3 and 4, pp.313-336, 1996.
[3] C.K. Chan and L.M. Cheng, ”Hiding data in images by simple LSB substitution”, Pattern Recognition 37,469-474, 2004.
[4] C.C. Chang and W.C. Wu, ”A steganographic method for hiding secret data using side match vector quantization, ”IEICE Trans.Inf.Syst.,vol. E88-D,no. 9,pp. 21592167,2005.
[5] C.C. Chang, W.L. Tai and C.C. Lin,”A reversible data hiding scheme based on side match vector quantization”IEEE trans. Image Process.,vol. 16,NO. 10,OCTOBER 2006.
[6] M. Celik, G. Sharma, A.M. Tekalp and E. Saber, “Reversible data hiding,” in Proceedins of the International Conference on Image Processing 2002,Rochester, NY, September 2002.
[7] J. Fridrich, M.Goljan and R. Du,”Invertible authentication watermark for JPEG images,”in Proc. ITCC, Las Vegas, NV, Apr. 2001, pp. 223-227.
[8] J. Fridrich, M. Goljan and R. Du, “Lossless data embedding-New paradigm in digital watermarking,” J.Appl. Signal Process., vol. 2002,no. 2,pp. 185-196,Feb. 2002.
[9] M. Jo and H.D. Kim, “A digital image watermarking scheme based on vector quantization,” IEICE Trans. Inf., vol. 62, no.3-4,pp. 275-289, Aug.2004.
[10] T. Kim, ”Side match and overlap match vector quantizers for images,”IEEE Trans. Image Prcess., vol. 1,no. 4,pp. 170-185, Apr. 1992.
[11] W.N. Lie and L.C. Chang, “Data hiding in images with adaptive numbers of least significant bits based on the human visual system”. Proc. IEEE Internat. Conf. Image Process. 1, 286–290 , 1999.
[12] E.T. Lin and E.J. Delp, “A review of data hiding in digital images” ,http://citeseer.nj.nec.com/lin99review.html
[13] G.C. Langelaar, I. Setyawan, and R.L. Lagendijk, “Watermarking digital image and video data. A state-of-the-art overview,” IEEE Signal Processing Magazine, vol. 17, no. 5,pp. 20-46,Sept. 2000.
[14] S.L. Li, K.C. Leung, L.M. Cheng and C.K. Chan ,”Data hiding in images by adaptive LSB substitution based on the value differencing”. Proc. IEEE ICICIC’06 2006.
[15] P. Moulin and R. Koetter ”Data-hiding codes,”Proceedings of the IEEE,93,(12):2083～2125, 2005.
[16] N. Provos and P. Honeyman, “Hide and Seek: An Introduction to steganography,” Security & Privacy Magazine ,IEEE, vol. 1, pp. 32-44, May-June 2003.
[17] G.K. Wallace, “The JPEG still picture compression standard,” IEEE Trans. Consumer Electronics, vol.38, no.1, pp. 18-34, Feb. 1992.
[18] R.Z. Wang, C. F. Lin and J.C. Lin, “Image hiding by optimal LSB substitution and genetic algorithm,” Pattern Recognition 34 (3) 671-683, 2001.
[19] H.C. Wei, P.C. Tsai and J.S. Wang,” Three-sided side match finite-state vector quantization.” IEEE Trans. Circ. Syst. Video Technol. 10 (1), 51–5800 , 2000.
[20] D.C. Wu and W.H. Tsai,” A steganographic method for images by pixel-value differencing”. Pattern Recognition Lett. 24, 1613–1626 , 2003
[21] X. Wu, “Lossless compression of continuous-tone image via context selection, quantization, and modelling” IEEE trans. on Image Proc., vol. 6, no. 5, pp. 656-664, May 1997.
[22] K. Okeya and K. Schmidt-Samoa, C. Spahn and T. Takagi, "Signed binary representations revisited," Springer-Verlag Lecture Notes in Computer Science, vol. 3152, pp. 123-139, 2004.
[23] F.A.P. Petitcolas, R.J. Anderson and M.G. Kuhn, “Information Hiding-A Survey,” Proc. IEEE, vol. 87, no. 7, pp. 1062-1078, July 1999.
[24] G..W. Reitwiesner. “Binary arithmetic,” Advances in Computers, vol. 1 pp. 231–308. Academic Press, 1960.
[25] M.D. Swanson, B. Zhu and A.H. Tewfik, ”Robust Data Hiding for Images,” Proc. IEEE Digital Signal Processing workshop, 1996.
[26] Y.Q. Shi, Z. Ni, D. Zou, C. Liang and G. Xuan, ”Lossless data hiding: fundamentals, algorithms and applications,” IEEE ISCAS 2004.
[27] S. Katzenbeisser and F.A. Petitcolas, ”Information hiding techniques for steganography and digital watermarking,”Artech House ,Boston London, pp. 15-40. 2000.
[28]”Information Technology-Digital Compression and Coding of Continuous-ton Still Image – Requirements and Guidelines” ITU-T Recommendation T.81, 1992 |ISO/IEC 10918-1:1993 International Telecommunications Union. (Commonly referred to as JPEG standard)
[29]“Data Encryption Standard(DES),” National Bureau of Standards (U.S.), Federal Information Processing Standards Publication 46, National Technical Information Service, Springfield, VA, April 1977.
[30] ISO/IEC JTC1 CD 11544: Coded representation of picture and audio information-progressive bi-level image compression, 1993.
[31] 賴溪松、韓亮、張真誠，近代密碼學及其應用。台灣：松崗電腦圖書資料股份有限公司，2001年10月。